udp socket 多线程通信问题。。急。。。。

namespace UDP服务器端
{
    public partial class Form1 : Form
    {
        private UdpClient server;
        private IPHostEntry ipHost = Dns.Resolve(Dns.GetHostName());
        private IPEndPoint receivePoint;
        private IPEndPoint sendPoint;
        private int port = 8008;
        private Thread startServer;        public Form1()
        {
            InitializeComponent();
            
        }
        public void start_server()
        {
            
            while (true)
            {
                
                //接收从远程主机发送到本地8080端口的数据                                          byte[] recData = server.Receive(ref receivePoint);
                ASCIIEncoding encode = new ASCIIEncoding();
                //server=new UdpClient(
                this.listBox1.Items.Add("接收数据："+recData[0]);
                byte[] sendData=new byte[2];
                sendData[0]=56;
                sendData[1]=52;
                listBox1.Items.Add( receivePoint.Address.ToString()+"   "+receivePoint.Port.ToString());
                server.Send(sendData, 2, receivePoint.Address.ToString(),int.Parse(receivePoint.Port.ToString()));
                
            }
        }
        public  void run()
        {
            server = new UdpClient(port);
            IPAddress address = ipHost.AddressList[0];
            receivePoint = new IPEndPoint(address, port);           
            startServer = new Thread(new ThreadStart(start_server));
            startServer.Start();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            listBox1.Items.Clear();
        }       
        private void Form1_Load(object sender, EventArgs e)
        {
            Form.CheckForIllegalCrossThreadCalls = false; 
            run();
            
        }
    }
}
以上是我的代码，，客户端我用socket  调试工具代替，，
放在同一pc上没有问题，不同pc就没任何现象。
请问这是哪里出了问题